1. Field of the Invention
The present invention relates to an information regenerating apparatus for an optical recording medium that regenerates information using an optical card as an optical recording medium.
2. Description of the Prior Art and Related Art
In an optical information recording/regenerating apparatus using an optical card as an optical recording medium, an optical card having multiple tracks, which are parallel with one another, and an optical head for optically recording or regenerating information on or from the optical card are moved relatively in the direction of extension of tracks to record or generate information.
In general, in an optical information recording/regenerating apparatus using a disk type optical medium such as an optical disk, rotation causes information to be recorded or regenerated. The speed of relative movement between the optical recording medium and optical head is relatively constant. On the contrary, in an optical information recording/regenerating apparatus using an optical card, the optical card is reciprocated to record and/or regenerate information. Therefore, the speed of relative movement between the optical card and optical head varies relatively largely. In this kind of optical recording/regenerating apparatus, when information is recorded and/or regenerated, the variation in speed must be taken into consideration. In particular, when information, which has been modulated using a modified frequency modulation (MFM) method, a (2, 7) modulation method, or other self-clock modulation method, then recorded, is to be generated, the variation in speed must be taken account to generate a bit clock for demodulation.
For example, in an apparatus described in Japanese Patent Laid-Open No.3-69069, the pulse spacings of pulses making up a binary-coded signal are measured and averaged to work out a reference period. Based on the reference period, a bit clock is generated and demodulated. Thus, a variation in speed is canceled out.
FIG. 1 is a circuit block diagram showing a major portion of an information regenerating apparatus described in the above patent publication.
The regenerating apparatus supplies a binary-coded signal to a pulse spacing sampling means 31 and to a synchronizing means 32. The pulse spacing sampling means 31 subsequently measures the pulse spacings of a train of pulses making up the binary-coded signal, then supplies the measured pulse spacings to a pulse multiple detecting means 33. The pulse multiple detecting means 33 detects how many times each of the pulse spacings sent from the pulse spacing sampling means 31 is as long as a reference period T, then supplies the detected multiples to a reference period calculating means 34. The reference period calculating means XY4 uses the pulse spacings of several pulses and their multiples relative to the reference period T to calculate a new reference period T', then supplies the reference period T' to a clock generating means 35. The reference period T' is also supplied as a reference period for detecting the next pulse multiple to the pulse multiple detecting means 33.
The reference period T' is an average obtained by dividing the sum of pulse spacings of several pulses by the sum of their pulse multiples.
The clock generating means 35 uses a period based on the reference period T' sent from the reference period calculating means 34 to generate a bit clock for demodulating a pulse train making up a binary-coded signal.
On the other hand, the synchronizing means 32 produces a required synchronizing signal using the binary-coded signal, the bit clock sent from the clock generating means 35, and the period T', then supplies the synchronizing signal to the clock generating means 35. The clock generating means 35 generates a bit clock so that the bit clock will be synchronized with the binary-coded signal at intervals of given pulse widths. This enables regeneration of a bit clock that moderately catches up with a variation in the speed of relative movement between an optical recording medium and a regeneration head.
FIG. 2 shows a curve plotted with the time on the axis of abscissas and with the speed of relative movement between an optical recording medium and a regeneration head on the axis of ordinates, indicating variations in the speed of relative movement.
When that pulse of a binary-coded signal at a point P is demodulated, assuming that a bit clock is generated using, as shown in FIG. 2, the pulse spacings of a pulse train of the binary-coded signal in a region R2 through which the binary-coded signal has passed before the point P. In this case, all average speed of relative movement between an optical recording medium and a regeneration head becomes V2. V2 differs from the speed of relative movement, V1, actually measured at the point P. To produce a correct bit clock in consideration of a variation in the speed of relative movement, pulse spacings of a pulse train making up a binary-coded signal and falling in a region R1 centered on the point P must be used in calculation to generate a bit clock.
In the foregoing apparatus described in the above patent publication, pulse spacings of a pulse train in a region R2 in FIG. 2 are used in calculation to generate a bit clock. This means that the period for a bit clock is determined based on a value difference from the speed of relative movement measured actually at the point P. A proved solution has not been presented on how to produce a precise bit clock, which is used for regenerating information correctly, by coping with a variation in the speed of relative movement between an optical recording medium and a regeneration head.
The grantee of the present invention, which is a corporation, has proposed a dual light source type optical information recording/regenerating apparatus having a photodetector constructed as shown in the related art of FIG. 3 by filing Japanese Patent Application No.3-260755.
The dual light source type optical information recording/regenerating apparatus comprises a light source for generating an information recording light beam and a light source for generating an information regenerating light beam which are independent of each other. While the information recording light beam is recording information on an optical recording medium, an information regenerating light beam regenerates the recorded information, and performs verification; that is, checks the acceptability of the recording.
For verification, a single light source type apparatus scans a light beam spot twice over tracks formed on an optical recording medium. Compared with the single light source type apparatus, the dual light source type apparatus permits an actual recording speed that is twice as fast.
The dual light source type apparatus can stabilize the quantity of light from the light source for information regeneration. Therefore, the information regenerating light beam can be used to produce a signal for focus servo control or tracking servo control. Therefore, while recording information, the dual light source type apparatus permits stable servo control.
FIG. 3 shows a construction of a photodetector employed for the dual light source type optical information recording/regenerating apparatus described in the aforesaid related art. In FIG. 3, a spot image of a recording light beam, and spot images of the zero-order diffracted light and first-order diffracted light of a regenerating light beam, which are projected on the photodetector, are drawn with solid lines, while the state of an optical recording medium opposed to the photodetector is drawn with dashed lines.
In FIG. 3, an alphanumeric character 23a denotes a spot image of an information recording light beam. 25b denotes a spot image of the zero-order diffracted light of an information regenerating light beam. 25e and 25f denote spot images of first-order diffracted light.
The photodetector includes signal regenerating light receiving elements 95, 96, and 97, and tracking light receiving elements 91, 92, 93, and 94, and receives light reflected from the spot image 23a. In the photodetector, a signal regenerating light receiving element 98 is installed at a position at which the image 25e of the spot 25d marked by the first-order diffracted light is formed.
In the photodetector having the foregoing construction, when information is regenerated normally, each pair of the tracking light receiving elements 91 and 92, and 93 and 94 detect a positional change of the image of a guide track resulting from displacement of a track as a variation in the quantity of received light, then generates a tracking error signal. Each of the signal regeneration light receiving elements 95, 96, and 97 detects the presence or absence of a pit on each of three tracks as a variation in the quantity of light, then detects a regenerative signal.
In information recording, when an optical card moves in an arrow-a direction (hereafter, forward direction), first, a pit 22a formed by the information recording light beam spot 23a is scanned by an optical head. Then, when the pit 22 reaches a position of the spot 25a, the signal regenerating light receiving element 95 provides an output signal. With the output signal, verification is carried out.
When the optical card 7 moves in an arrow-b direction (hereafter, reverse direction), first, a pit 22 formed by the information recording light beam spot 23 is scanned by the optical head. Then, when the pits 22 reaches the position of the spot 25b, the signal regenerating light receiving element 98 provides an output signal. With the output signal, verification is carried out.
As mentioned above, according to the construction of the photodetector, in whichever direction the optical card moves; in the forward or reverse direction, a regenerative signal can be produced immediately after recording.
When the optical card moves in the forward direction, an output signal of the light receiving element 95 that detects an image of the spot 25d preceding the information recording light beam spot 23a is checked to recognize the state of a track on which the image is to be recorded. When the optical card moves in the reverse direction, an output signal of the light receiving element 98 that detects an image of the spot 25e preceding the information recording light beam spot 23a is checked to recognize the state of a track on which the image is to be recorded. Thus, the state of a track can be recognized immediately before information is recorded.